linux-kernel - Re: [PATCH v2 3/4] iommufd: Destroy vdevice on idevice destroy

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Message-ID: <e8977169-e1f6-4ba4-931b-9bebffc1469f@linux.intel.com>
Date: Wed, 25 Jun 2025 09:55:47 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, Xu Yilun
 <yilun.xu@...ux.intel.com>, "jgg@...dia.com" <jgg@...dia.com>,
 "jgg@...pe.ca" <jgg@...pe.ca>, "will@...nel.org" <will@...nel.org>,
 "aneesh.kumar@...nel.org" <aneesh.kumar@...nel.org>
Cc: "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "joro@...tes.org" <joro@...tes.org>,
 "robin.murphy@....com" <robin.murphy@....com>,
 "shuah@...nel.org" <shuah@...nel.org>,
 "nicolinc@...dia.com" <nicolinc@...dia.com>, "aik@....com" <aik@....com>,
 "Williams, Dan J" <dan.j.williams@...el.com>, "Xu, Yilun"
 <yilun.xu@...el.com>
Subject: Re: [PATCH v2 3/4] iommufd: Destroy vdevice on idevice destroy

On 6/24/25 16:12, Tian, Kevin wrote:
>> From: Baolu Lu <baolu.lu@...ux.intel.com>
>> Sent: Tuesday, June 24, 2025 11:32 AM
>>
>> On 6/23/25 17:49, Xu Yilun wrote:
>>> Destroy iommufd_vdevice(vdev) on iommufd_idevice(idev) destroy so that
>>> vdev can't outlive idev.
>>>
>>> iommufd_device(idev) represents the physical device bound to iommufd,
>>> while the iommufd_vdevice(vdev) represents the virtual instance of the
>>> physical device in the VM. The lifecycle of the vdev should not be
>>> longer than idev. This doesn't cause real problem on existing use cases
>>> cause vdev doesn't impact the physical device, only provides
>>> virtualization information. But to extend vdev for Confidential
>>> Computing(CC), there are needs to do secure configuration for the vdev,
>>> e.g. TSM Bind/Unbind. These configurations should be rolled back on idev
>>> destroy, or the external driver(VFIO) functionality may be impact.
>>>
>>> Building the association between idev & vdev requires the two objects
>>> pointing each other, but not referencing each other.
>>
>> Does this mean each idevice can have at most a single vdevice? Is it
>> possible that different PASIDs of a physical device are assigned to
>> userspace for different purposes, such that there is a need for multiple
>> vdevices per idevice?
>>
> 
> PASID is a resource of physical device. If it's reported to a VM then
> it becomes the resource of virtual device. 1:1 association makes
> sense here.

Okay, make sense.